Summary Report / April 2014 Land Subsidence from ... · Summary Report / April 2014 Land Subsidence from Groundwater Use in California Acknowledgement The California Water Foundation

Prepared By

Summary Report / April 2014

Land Subsidence from Groundwater Use in California

James W. Borchers • Michael Carpenter

With Support By



Contributing Authors

• James W. Borchers• Vicki Kretsinger Grabert• Michael Carpenter• Barbara Dalgish• Debra Cannon

California Water Foundation The California Water Foundation (CWF) seeks to transition California to a sustainable and resilient water future – a future in which water is managed as a natural resource, looking across all sources and uses to find the best solutions for social welfare, economic development, and environmental sustainability. CWF supports innovative projects and policies that address water challenges today, while achieving long-term, science-based solutions for the future. CWF is an initiative of Resources Legacy Fund, with primary funding from S.D. Bechtel, Jr. Foundation and Pisces Foundation, and additional support from David and Lucile Packard Foundation and others. Learn more at: http://www.californiawaterfoundation.org.



Acknowledgement

The California Water Foundation Subsidence Resources Group was established on April 29, 2013 to act as advisors for this report and is made up of those persons most knowledgeable on the subject of subsidence. The group has provided general input and subsequent review of reference lists, data assessments, and descriptions of monitoring and research needs. CWF appreciates the contributions of the 22 members listed below:

Gerald Bawden U.S. Geological Survey

Chris Bonds CA Dept. of Water Resources No. Central Region

Rob Carruth U.S. Geological Survey

Wes Danskin U.S. Geological Survey

Bill Ehorn CA Dept. of Water Resources Northern Region

Claudia Faunt U.S. Geological Survey

Devin Galloway U.S. Geological Survey

Randy Hanson U.S. Geological Survey

Carl Hauge CA Dept. of Water Resource (retired)

Donald C. Helm USGS/LLNL/CSIRO/UNR/NBMG/MSU (retired)

Charles Heywood U.S. Geological Survey

Thomas Holzer U.S. Geological Survey

Marti Ikehara USGS/NGS (retired)

Steven Ingebritsen U.S. Geological Survey

John Kirk CA Dept. of Water Resources So.Central Region

Stan Leake U.S. Geological Survey

Steven Phillips U.S. Geological Survey

Don Pool U.S. Geological Survey

Keith Prince U.S. Geological Survey (retired)

Francis S Riley U.S. Geological Survey (retired)

Eric Senter CA Dept. of Water Resources

Michelle Sneed U.S. Geological Survey


Land Subsidence from Groundwater Use in California Table of Contents

Executive Summary

Introduction

1.0 Groundwater Extraction and Subsidence – Page 6

2.0 Examples of Subsidence from Groundwater Extraction In California – Page 9

2.1 Santa Clara Valley 2.2 San Joaquin Valley 2.2.1 Historical Subsidence in the San Joaquin Valley 2.2.2 Current Subsidence in the San Joaquin Valley 2.3 Sacramento Valley 2.4 Antelope Valley 2.5 Coachella Valley 2.6 Mojave River Basin and Vicinity

3.0 Measuring and Monitoring Land Subsidence – Page 31

3.1 Surveying and the Global Positioning System 3.2 Satellite Synthetic Aperture

Radar Interferometry (InSAR) 3.3 LiDAR 3.4 Borehole Extensometers

4.0 Recommendations – Page 34 4.1 Monitor Land Surface Elevation

Changes and Compaction 4.2 Monitor Ancillary Factors:

Groundwater Levels and Drillers’ Reports 4.3 Collect, Store and Disseminate Data 4.4 Evaluate and Prioritize Subsiding

Groundwater Basins

References cited are available in the full report found online at www.californiawaterfoundation.org

APRIL, 2014 SUMMARY REPORT Land Subsidence from Groundwater Use in California

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LSCE, BORCHERS AND CARPENTER 1

EXECUTIVE SUMMARY

California’s groundwater is a vital resource for the state that provides water supplies for urban

and rural areas, supports a large agricultural economy, and benefits fish and wildlife habitats and

ecosystems. Groundwater meets about 40 percent of the state’s water demands in an average

year. During droughts when surface supplies are limited, groundwater offers a critical buffer,

providing a higher percent of the state’s water supply. In 2014, it is anticipated statewide

groundwater use will be closer to 65 percent because of the critical nature of this year’s drought.

Historically, groundwater has been pumped as needed in many areas of the state, often with little

regard for the deleterious effects of over pumping. Over pumping is not sustainable in the long-

term and can lead to a number of adverse consequences, including water-quality degradation;

increased energy costs for groundwater pumping; costs for well deepening or replacement;

impacts to nearby rivers and streams; and land subsidence. This report highlights the current and

historical impacts of land subsidence in California due to groundwater pumping and makes

recommendations for monitoring and assessment. The purpose of this report is to summarize

knowledge about the extent and costs of subsidence so that this information can be part of a

larger discussion on sustainable groundwater management in California.

This report confirms that land subsidence in California is not just an historical occurrence, but

that it is an ongoing problem in many regions. The report presents key examples of significant

historical subsidence and current active occurrences of subsidence, including the impacts and

costs.1

There is no comprehensive land subsidence monitoring program in California. The information

in this report was compiled from individual regional or local studies, which usually were

initiated after substantial subsidence impacts had occurred. The most comprehensive evaluation

of land subsidence in California occurred between 1955 and 1970, to assist with the construction

of the state and federal water projects. Funding for this program ended soon after completion of

the state and federal water projects. The lack of comprehensive subsidence monitoring has had

costly consequences for the state.

Land subsidence has been discovered in many areas of the state, causing billions of dollars of

damage. Impacts from subsidence fall into the following categories:

loss of conveyance capacity in canals, streams and rivers, and flood bypass channels;

diminished effectiveness of levees;

1 The full report can be found at: Luhdorff & Scalmanini, Consulting Engineers, James Borchers, and Michael

Carpenter. 2014. Report of Findings: Land Subsidence from Groundwater Use in California.


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damage to roads, bridges, building foundations, pipelines, and other surface and

subsurface infrastructure; and

development of earth fissures, which can damage surface and subsurface structures and

allow for contamination at the land surface to enter shallow aquifers.

This report summarizes six major areas of subsidence in California. In many of these regions

subsidence continues today, sometimes at nearly historically high rates of more than 1 foot/year

(ft/yr). This report provides examples of current and historical subsidence pieced together from

local or regional studies that were conducted by state, federal, or local agencies after subsidence

was discovered to have dramatically deformed the land surface and/or caused significant

infrastructure problems.

Santa Clara Valley

o Subsidence in Santa Clara Valley, in the South San Francisco Bay Area, has required

diking to prevent flooding from the bay; water well, and sanitary and storm sewer system

repairs; modifications to roads, bridges, and stream channel levees, and other

infrastructure construction and repair, translating to more than $756 million in damages.

o Between 1910 and 1995, downtown San Jose subsided 14 feet.

o Santa Clara Valley Water District essentially halted inelastic subsidence in the region by

implementing a monitoring program, importing surface water, and artificially recharging

groundwater. Groundwater pumpers report usage to the District. The District issues

permits for wells and collects a groundwater production charge to recover those costs.

San Joaquin Valley

o Subsidence from groundwater extraction in the San Joaquin Valley has been called the

greatest human alteration of the Earth’s surface.

o By 1970, subsidence of more than 1 foot had affected 5,200 mi2—more than half of the

valley—and in some areas it had reached 28 feet.

o Over the past decade, subsidence has been identified in two regions in the San Joaquin

Valley, including more than 4 feet during a 3½ year period near Corcoran, California.

o Subsidence has caused major impacts to infrastructure and physical features, including

the San Joaquin River, Delta-Mendota Canal, Friant-Kern Canal and San Luis Canal, as

well as numerous privately owned canals and related infrastructure such as turnouts,

bridges, pipelines, and storm sewers.

o These costs, add up to a total estimated cost of more than $1.3 billion during 1955-1972

(2013 dollars). Subsequent cost data are unavailable.


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Sacramento Valley

o Subsidence in the Sacramento Valley has resulted in wide scale destructive failure of

steel groundwater well casings, making wells sometimes unusable.

o From the locations of damaged wells during a drought in 1976-1977, the subsidence

appears to stretch from central Colusa County, through Yolo County, to Dixon in Solano

County.

Antelope Valley

o Subsidence in Antelope Valley, east of Los Angeles, has been occurring for over 80

years. Increased pumping in the last 30 years due to population growth has accelerated

the groundwater level declines to as much as 300 feet in some areas.

o Subsidence has adversely affected runways at Edwards Air Force Base and caused other

negative consequences such as increased flooding and erosion; failed well casings; and

damage to roads, homes, and other structures.

Coachella Valley

o Subsidence in Coachella Valley, in Riverside County, paused after importation of surface

water began in 1949, but resumed in the 1970s as population and groundwater pumping

increased.

o Earth fissures formed in 1948 and again recently. A subsidence study of a portion of the

Coachella Branch of the All American Canal showed that the canal subsided as much as

1.35 feet from 1995 to 2010.

Mojave River Basin Area

o In the Mojave River Basin area, groundwater pumping resulted in groundwater-level

declines of more than 100 feet. Giant desiccation cracks, sink-like depressions, and earth

fissures more than 3 feet wide and deep have made permanent scars on the landscape.

o A 1998 survey indicated 2 to 5 feet of subsidence occurred in Lucerne Valley.

o Recent groundwater adjudication developed actions to stabilize the water levels of the

basin and manage groundwater pumping.

As indicated in this report, alarming rates of subsidence continue to occur throughout California,

causing impacts and costs that can have lasting effects to property and the environment. This

information is only being collected after the impacts from subsidence have occurred. The lack of

a coordinated subsidence monitoring program, uniform monitoring procedures, and an ongoing

data repository is causing significant irreversible impacts and costs to many regions and the state.

This report proposes the following recommendations to help California address the ongoing

economic and environmental impacts associated with over extraction of groundwater and the

resulting land surface subsidence.


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Monitor Land Surface Elevation Changes and Compaction

Characterize Aquifer System and Monitor Groundwater Levels

Collect, Store and Disseminate Subsidence and Groundwater Data

Prioritize and Evaluate Subsiding Groundwater Basins


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In an average year, groundwater

provides about 40% of the state’s

water supply; in the current drought, it

is expected to be 65% or more.

INTRODUCTION

As California contends with possibly the worst drought on record, the condition of the state’s

groundwater basins takes on increased importance. California’s groundwater is a vital resource

for urban, rural and agricultural water users, and for the health of aquatic ecosystems and

biological habitats. Groundwater basins underlie 40 percent of California. In an average year,

groundwater provides about 40 percent of the state’s water supply; in drought years, it may

provide 65 percent or more. In many basins, groundwater is the principal source of supply.

Groundwater levels in some areas of California are declining past historical lows. Projected

population increases, along with

alteration of precipitation patterns due to

climate change, will put added stress on

groundwater resources in the state.

Historically in California, groundwater

has been pumped as needed, often with

little regard for the deleterious effects of over pumping. Chronically declining groundwater

levels can lead to a number of adverse consequences, including saltwater intrusion or other water

quality degradation; reduced groundwater storage, availability and reliability; increased energy

costs; facilities costs for well deepening or replacement; streamflow depletion; environmental

effects; and land subsidence. This report highlights issues and key findings related to land

subsidence in California due to groundwater extraction2,3

When groundwater pumping chronically exceeds recharge, a long-term decline of groundwater

levels usually results. This can lead to inelastic compaction of the aquifer system, permanent

subsidence of the land surface, and even earth fissures. Some of the more costly consequences of

subsidence include:

coastal flooding

increased extent and depth of inland flooding

reduced freeboard and carrying capacity of canals, aqueducts, rivers and flood bypass

channels

damage to buildings, roadways, bridges, pipelines, canals, aqueducts, levees, sewerages,

and wells; and

increased sediment erosion or deposition and impairment of leveled agricultural fields

2The full report can be found at: Luhdorff & Scalmanini, Consulting Engineers, James Borchers, and Michael

Carpenter. 2014. Report of Findings: Land Subsidence from Groundwater Use in California. 3References are contained in the full report.


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Recent observations of subsidence in the

San Joaquin Valley are unanticipated and

alarming, and likely to continue unless

changes occur.

As described below, significant subsidence has occurred historically in the San Joaquin Valley

and elsewhere in California, creating substantial economic costs. Indeed, the cost of remediating

subsidence in the San Joaquin Valley alone during 1955-1972 was estimated to be over $1.3

billion in 2013 dollars not including the significant damage to canals, river levees, and flood

channels. This is not merely a historical issue. Recent observations of subsidence in the San

Joaquin Valley are unanticipated and

alarming, and likely to continue unless

changes occur. The purpose of this

report is to summarize knowledge

about the extent and costs of

subsidence so that this information can

be part of a larger discussion on

sustainable groundwater management

in California.

A review of published literature revealed that there is no single compilation of historical and

active occurrences of subsidence in the state. Although this report is not an exhaustive detailing

of every occurrence of groundwater extraction-related subsidence in California, it presents key

examples of significant historical and active subsidence, including the impacts and costs. A more

detailed inventory is presented in the full report (Luhdorff and Scalmanini Consulting Engineers,

et al., 2014, Report of Findings: Land Subsidence from Groundwater Use in California)

California lacks a coordinated statewide subsidence monitoring program, uniform monitoring

and analysis procedures, and an accessible repository for subsidence-related data, which are

essential to the assessment of subsidence. Furthermore, the state lacks funding to support

technical synthesis and evaluation of data and remotely sensed imagery. Legislative and policy

changes are needed to address this ongoing problem that has immense economic and

environmental implications for the state of California.

The report is organized into the following sections: Section 1 explains subsidence processes

related to groundwater extraction. Section 2 offers examples of subsidence as a result of

groundwater extraction in California. Section 3 describes methods used to measure the

magnitude of land subsidence and ground-surface deformation, and Section 4 presents

recommendations related to subsidence monitoring and sustainable groundwater management.

1.0 GROUNDWATER EXTRACTION AND SUBSIDENCE

A balance occurs naturally in an undeveloped aquifer system where recharge and discharge of

groundwater are equal. As seen in Figure 1, an aquifer system consists of layers of gravel, sand,

silt, and clay deposited by streams and rivers or in lakes or wetlands. Coarse-grained materials


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such as sand and gravel transmit water readily; fine-grained materials such as clay and silt

impede the movement of water. Groundwater pumping changes the water balance of the aquifer

system (Galloway et al., 1999), deforms the land surface and may create permanent land

subsidence. In particular, when water is drained from clays, permanent subsidence will result

because much of the water drained cannot be replaced. This permanent deformation, called

inelastic or non-recoverable compaction, is responsible for permanent or non-recoverable land

subsidence (Hoffmann et al, 2003) (Figure 2). Inelastic compaction occurs when the structure of

the clays is compromised during compaction, such that it is unable to expand to its original

thickness even when groundwater levels rise to pre-pumping levels.

Figure 1. An undeveloped aquifer system in balance (adapted from Galloway et al., 1999)


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Groundwater pumping is

responsible for most subsidence in

California.

Figure 2. Land subsidence due to compaction of fine-grained material after fluid extraction (adapted from

Sneed and Galloway, 2000).

Aquifer-system compaction caused by groundwater pumping and extensive water-level declines

is responsible for most subsidence in California and has been observed for decades in the Santa

Clara Valley, San Joaquin Valley, Sacramento Valley, Antelope Valley, and elsewhere.

The relative timing of changes in groundwater levels and aquifer-system compaction is complex.

Residual compaction may continue long after

water levels have stabilized in the aquifers.

An example of this residual compaction is at

Edwards Air Force Base in Antelope Valley,

California, where the ongoing long-term

effects of delayed yield from thick, slowly draining, clayey, confining units continues in

response to large water-level declines that occurred between 1950 and 1975 (Sneed and

Galloway, 2000).


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Subsidence may continue long after

water levels have stabilized in the

aquifers.

In over-pumped, confined aquifer

systems, water provided during inelastic

compaction of clayey layers typically

amounts to between 10 and 30 percent of

the total volume of water pumped (Riley,

1969). Water of compaction is available

only once—usually beginning when the aquifer system experiences historically low water levels.

Water of compaction is akin to a sequestered inheritance, such as a chest of rare coins buried

deeply out of sight. It is not invested, so it gathers no interest, although its value can fluctuate

with market forces and the costs to retrieve it. It is available only once, so its expenditure should

be planned carefully. In California, water of compaction has supported a vibrant agricultural

industry and expanding population. It can be argued, though, that its use has not been carefully

planned; a legacy of aquifer-system compaction, land subsidence, and unanticipated deleterious

effects on surface and subsurface infrastructure has resulted.

Water managers have to deal with long-term water supply and economic issues created by

inelastic compaction of thick confining units. Inelastic compaction permanently reduces the

amount of storage space for water in the aquifer system. After an initial period of inelastic

compaction and subsequent water-level recovery, extracting an identical amount of water during

a second pumping cycle will result in lower water levels than during the first cycle of pumping.

This occurs for two reasons—because 1) less water is stored in the aquifer system due to

irreversible removal of water from now-collapsed clays and fine-grained materials, and 2)

compaction during the first pumping cycle inhibits the ability of water to drain from confining

units and clayey interbeds by decreasing their permeability4. Lowering water levels further, to

produce the same volume of water initially retrieved, will induce additional inelastic compaction

and land subsidence. The manager will have to contend with inelastic compaction each pumping

cycle. The energy expended, and the pumping costs to lift groundwater to the surface, will

increase as water levels drop farther.

2.0 EXAMPLES OF SUBSIDENCE FROM GROUNDWATER

EXTRACTION IN CALIFORNIA

Groundwater extraction from nearly any aquifer will cause some degree of subsidence as aquifer

materials adjust to new stresses. In fact, any change of groundwater levels from any cause,

natural or human induced, will deform the land surface, moving it up or down in response to

expansion or compression of aquifer materials. Substantial and damaging subsidence from

4 Permeability is the ease with which water moves through a material. Sand and gravel have high permeability; clay

has very low permeability.


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groundwater extraction in California is nearly always related to inelastic compaction in an

aquifer system, or to differences in the magnitude of compaction over short lateral distances.

In California, subsidence has resulted in expensive remediation to address loss of conveyance

capacity in canals, streams and rivers, flood bypass channels, diminished levee effectiveness, and

damage to roads, bridges, building foundations, pipelines, and other surface and subsurface

infrastructure. Development of earth fissures has damaged surface and subsurface structures and

also provided conduits for contamination at the land surface to enter shallow aquifers, degrading

groundwater resources.

Subsidence is occurring today at nearly historically high rates (almost 1 ft/yr) in some areas.

Even so, the location of all subsiding areas and the magnitude of subsidence throughout the state

cannot be determined by reviewing published reports or databases because California does not

have a coordinated statewide monitoring and reporting program for land subsidence. Therefore,

instead of a comprehensive description of this statewide phenomena, the following sections

provide examples pieced together from local or regional studies, some ongoing but mostly

historical, that were conducted by state, federal, or local agencies after subsidence was

discovered to have reached alarming proportion.

Summaries of such subsidence in the Santa Clara Valley, San Joaquin Valley, Sacramento

Valley, Antelope Valley, Coachella Valley, and Mojave River Basin and vicinity follow. More

information on each of these and other areas, as identified in Figure 3, is included in the full

report (Luhdorff and Scalmanini Consulting Engineers, et al., 2014, Report of Findings: Land

Subsidence from Groundwater Use in California).


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Figure 3. Areas of subsidence caused by groundwater extraction in California. (Historic subsidence

occurred before 1993.)


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The estimated cost of subsidence

remediation in the Santa Clara Valley

translates to more than $756 million in

2013 dollars.

Between 1910 and 1995, downtown

San Jose subsided by 14 feet.

2.1 Santa Clara Valley

The northern Santa Clara Valley, an alluvial lowland at the south end of the San Francisco Bay,

was the first area in the United States where land subsidence due to groundwater overdraft was

recognized and described (Tolman and Poland, 1940). It is also the first area where remedial

action effectively halted the substantial inelastic subsidence caused by massive withdrawals of

groundwater that supplied water first for agricultural development and later primarily for

domestic and industrial uses.

Agriculture in this region developed rapidly

in the early 1900s; two thirds of the valley

was irrigated by 1920. Subsidence was first

noted in 1933, when bench marks installed in 1912 were found to have subsided more than 3 feet

(Fowler, 1981)5. Between 1910 and 1995, subsidence was greatest (14 feet) in downtown San

Jose, and about 100 mi2 of land had subsided by more than one foot. As a result, the Santa Clara

Valley Water District (SCVWD) now manages the aquifer system within tight water-level and

subsidence tolerances designed to prevent the reoccurrence of land subsidence.

Aquifer compaction that occurred in the Santa Clara Valley was inelastic, and land subsidence is

permanent. The importation of surface water, construction of artificial groundwater recharge

facilities, comprehensive subsidence monitoring networks, and efficient and coordinated

management of groundwater and surface-water supplies by a single water purveyor (the

SCVWD), allowed groundwater levels to return nearly to predevelopment levels in the Santa

Clara Valley and essentially stopped inelastic subsidence by 1969-1970.

The economic costs of subsidence in

California are perhaps nowhere

documented as thoroughly as in the

Santa Clara Valley. Because the

valley has a gentle topographic slope

and borders the San Francisco Bay,

the effects of subsidence on coastal flooding are dramatic. Were it not for levees at the bay shore

and bordering the streams and drains that flow to the bay, about 19 mi2 of the Santa Clara Valley

would be under water. The growing threat of flooding likely spurred initial recognition of the

subsidence issues.

5Units are provided in metric and English in the full report; for simplicity the Summary Report includes only

English units.


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Land subsidence from groundwater

extraction in the San Joaquin Valley has

been called the greatest human

alteration of the Earth’s surface.

Roll (1967), Viets and others (1979), and Fowler (1981) estimated the direct costs of subsidence

remediation activities in the Santa Clara Valley, including repairing water wells damaged or

destroyed during 1960-1965, building and operation of sanitary and storm sewers and pumping

stations where waste fluids no longer flowed easily by gravity, building bayfront dikes and

stream channel levees to prevent flooding, and raising bridges and roads. Translated to 2013

dollars, these costs totaled $756 million. Additional costs included replacing destroyed wells or

repairing wells at times other than 1960-1965, raising 50 miles of levees protecting 30 mi2 of

privately owned salt evaporation ponds, de-silting stream channels in flood-prone areas,

repairing flood damaged roads, moving flooded railroad tracks, or property values lost by flood

zone designation or levee-obstructed views.

Although subsidence has been halted in the Santa Clara Valley, considerable effort and expense

are expended annually to deal with its legacy. Strict subsidence monitoring programs assure that

these continuing investments are not wasted.

2.2 San Joaquin Valley

Land subsidence from groundwater

extraction in the San Joaquin Valley has

been called the greatest human alteration of

the Earth’s surface (Galloway et al., 1999).

It is inexorably linked to the development

of agriculture and the availability of water.

Agriculture in the San Joaquin Valley developed a reliance on the aquifer system because the

region is semi-arid; streamflow into the east side of the valley varies substantially from year to

year and is mostly not available on the west side. More than half of the thickness of the aquifer

system in the valley is composed of fine-grained sediments, including clays, silts, and sandy or

silty clays (Williamson et al., 1989) that are susceptible to compaction if depressured by

pumping wells.

Subsidence related to groundwater withdrawal in the valley began in the mid-1920s and

increased as agricultural development intensified after World War II. Subsidence rates eventually

exceeded 1 ft/yr in some places. Eventually groundwater levels in the deep aquifer system on the

west side of the valley declined by more than 400 feet. By 1970, subsidence of more than 1 foot

had affected 5,200 mi2—more than half of the valley—and subsidence southwest of Mendota

exceeded 28 feet (Poland et al., 1975) (Figure 4).

Despite early recognition of the relation between groundwater-level decline and subsidence near

Delano (Ingerson, 1940), subsidence from groundwater overdraft was not investigated regionally

until the early 1950s, when government agencies became concerned about a 30 percent reduction


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By 1970, subsidence of more than 1

foot had affected 5,200 mi2—more

than half of the valley—and

subsidence southwest of Mendota had

exceeded 28 feet.

in the design capacity of the San Joaquin River, about the effect of subsidence on the Delta-

Mendota Canal which was under construction, and on the California Aqueduct which was in the

planning stages. Part of the reason for the delayed reaction to subsidence is that it occurred

uniformly and over such a broad area that few residents or agencies realized that it had

happened.

In 1954, a Federal-State interagency

committee and the United States Geological

Survey (USGS) “Mechanics of Aquifers

Project” began studying land subsidence by

conducting both field monitoring and

research. The studies identified the

magnitude and extent of subsidence and its

quantitative relationship to groundwater overdraft, and developed new monitoring methods and

techniques for analysis of field data that allowed accurate computer models of aquifer system

compaction to be built. This provided information that allowed optimal siting of the California

Aqueduct, which along with the Delta-Mendota Canal and the Friant-Kern Canal, brought

surface water into the valley to diminish reliance on groundwater. Imported surface water

decreased reliance on the aquifer system. Groundwater levels recovered more than 200 feet in

some areas. Subsidence slowed and eventually stopped, reoccurring during subsequent droughts

and regulatory reductions in surface water diversions.

Figure 4. Joseph Poland standing near a pole

depicting more than 29 feet of land subsidence

between 1925 and 1977 in the San Joaquin

Valley southwest of Mendota (Ireland and others,

1984).


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Comprehensive leveling surveys of the valley ended in 1970; and, over time, funding for

coordinated subsidence investigations also ended, and field installations such as borehole

extensometers and water-level monitoring wells were decommissioned or fell into disrepair. The

California Department of Water Resources (DWR) continued to collect compaction data from a

few extensometers and from deep monitoring wells where available, and state, federal, and local

water agencies continued to run surveys on canal alignments intermittently, but analysis of this

information has not been coordinated.

2.2.1 Historical Subsidence in the San Joaquin Valley

Specific instances and costs of historical subsidence in the San Joaquin Valley include the

following:

Delta-Mendota Canal—Repairs to submerged canal service turnouts, drain inlets, bridges,

pipelines, check structures, embankments and concrete linings. Subsidence has impacted

about 30 miles of the Delta-Mendota Canal upstream from its terminus at Mendota Pool

by submerging canal service turnouts, drain inlets, bridges, pipelines, and check

structures used to control water surface elevation in the canal, and by overtopping the

concrete lining of the canal, reducing embankment freeboard, and flow capacity (Figure

5C). The United States Bureau of Reclamation (USBR) raised embankments and bridges,

and relocated pipeline crossings, and they and the San Luis Delta Mendota Water

Authority made other repairs and modifications. Using 1977 as the base year for these

repairs, the cost of USBR repairs in 2013 dollars is conservatively estimated as $30

million. (Prokopovich (1969, 1973, and 1986), Prokopovich and Herbert (1968) and

Prokopovich and Marriot (1983))

Outside Canal—Costs to raise embankments, bridges, turnouts, and weirs. Expensive

physical infrastructure problems have been caused by land subsidence in the Mendota

area. The flow capacity of the Central California Irrigation District’s Outside Canal has

been reduced 45 percent at the partly submerged Russell Avenue bridge (Figure 6).

Embankments were raised on the Outside Canal in 1971 and 1994, and improvements are

still continuing. Total costs for subsidence remediation on the Outside Canal are expected

to exceed more than $8.2 million.

Friant-Kern Canal—Repairs to canal berms, pumping plants, bridges, concrete linings,

canal turnouts, drains, and inlets. About 30 miles of the Friant-Kern Canal were impacted

by subsidence in the Tulare-Wasco area. Between the date construction was completed in

1951, and January 1975, parts of the affected reach of the canal subsided 5.5 feet,

interfering with operational activities (Prokopovich, 1983). Measurements of water depth

at closed check dams indicated that subsidence also affected parts of the canal farther

south toward Bakersfield. During 1976-1980 a 16.67 mile reach of the canal was

rehabilitated. Canal berm materials were excavated and re-compacted, concrete linings


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The [direct] cost of subsidence in the San

Joaquin Valley during 1955-1972 was

estimated to be more than $1.3 billion in

2013 dollars.

were extended upward, bridges were raised, canal turnout structures and drain inlets were

modified, and three large pumping plants were raised on new foundations. Costs for the

remedial activities in 2013 dollars totaled $15 million (calculated from 1976, 1977, and

1980 contract amounts provided in Prokopovich, 1983).

San Luis Canal—Raising of canal linings, bridges, and other canal structures, as well as

the rehabilitation of roads. The San Luis Canal, a jointly used feature of the federal

Central Valley Project and the California State Water Project that was completed in 1968,

has been affected by subsidence along 85 miles of its length between the Los Banos and

Kettleman City areas. The canal, now considered the middle section of the California

Aqueduct, passes through three major subsidence bowls: 1) southwest of Mendota, 2)

near the town of Cantua Creek, and 3) near the town of Huron (Ireland and others, 1984).

Because subsidence due to groundwater extraction had adversely affected the earlier-built

Delta-Mendota Canal, designers incorporated as much as 10 feet of extra freeboard into

the San Luis Canal, adding $30.7 million (2013 dollars) to construction costs. Additional

subsidence required additional raising of canal linings, bridges, and other canal structures

and rehabilitation of roads at costs of $1.6 million, $4.7 million, and $4.5 million,

respectively, during 1982, 1983, and 1984 (Prokopovich and Marriot, 1983). Adjusting

for inflation, these costs amounted to $55.7 million in 2013 dollars. Total construction

costs to account for subsidence were $86.4 million.

The total cost to the government to account for or repair subsidence damage to major

public canals and drains in the San Joaquin Valley was $133.86 million (2013 dollars).

These are contract construction costs and do not include costs for design, inspection, or

studies. They also do not include the considerable cost of precompacting the San Luis

Canal and major lateral canal alignments by diking and flooding to avoid subsidence

caused by hydrocompaction of moisture deficient soils in the western San Joaquin

Valley.

In addition to these costs to the

government, additional costs

such as well replacement were

borne by farmers and irrigation

districts. According to Wilson

(1968), 275 wells were reported with failed casings due to subsidence-induced damage in

the 618 mi2 region of maximum subsidence in the valley during 1950-1961. Current costs

to replace an 18-in diameter agricultural well average $200-$250 per foot (Scott Lewis,

Luhdorff and Scalmanini Consulting Engineers, oral comm. November 20, 2013). A

conservative cost estimate to replace these wells, assuming each well is about 1,600 feet

deep, is $90 million dollars (2013 dollars).


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Figure 5. A) Recent subsidence in the central San Joaquin Valley near El Nido between January 2007 and

March 2011. Cross sections A-A’ and B-B’ are shown in Figures 5B and 5C, respectively. (InSAR

derived subsidence data were provided as preliminary unpublished data courtesy of NASA-JPL).


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Figure 5. B) Elevation changes between 1972 and 2004 computed from repeat geodetic surveys along

Highway 152. (Modified from Sneed et al., 2013, Fig. 17).

Figure 5. C) Elevation changes between 1935 and 2001 along the Delta-Mendota Canal (modified from

Sneed et al., 2013, Fig. 17).


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Recent InSAR analyses show two

large areas in the San Joaquin Valley

currently subsiding substantially.

Figure 6. The partly submerged Russell Avenue bridge over the Outside Canal north of Mendota,

California. Before subsidence, canal inspections by Central California Irrigation District staff were

conducted from a boat passing under the bridge.

When costs of lost property value due to condemnation, re-grading irrigated land, and

replacement of irrigation pipelines and wells in subsiding areas are considered, the economic

cost of subsidence in the San Joaquin Valley was estimated to be $1.3 billion in 2013 dollars

during 1955-1972 (Gilbert Bertoldi, USGS (ret.), written commun., November 29, 2013). No

estimates of the indirect costs of land subsidence, such as flooding and long-term environmental

effects, have been made. Costs to repair canals also are not included in Bertoldi’s estimates.

2.2.2 Current Subsidence in the San Joaquin Valley

The current drought and changes to cropping

patterns from row crops and rangeland to

tree and other permanent crops have again

forced reliance on aquifer systems in the San

Joaquin Valley for agricultural irrigation

supplies. Recent Interferometric Synthetic Aperture Radar (InSAR) analyses show that two large

areas (Figure 7) in the San Joaquin Valley are currently subsiding substantially (Thomas Farr,


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Figure 7. Recent subsidence in the central and southern San Joaquin Valley. Subsidence in the

southern subsidence bowl is during 2007-2010, and in the northern subsidence bowl during 2007-

2011. Recently subsiding areas are distant from the point of maximum historical subsidence during

1926-1970. (InSAR derived subsidence data were provided as preliminary unpublished data courtesy

of NASA-JPL).


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Subsidence rates in the central San

Joaquin (El Nido) area are currently

about 20 times the rate of historical

subsidence in this area.

NASA-JPL, written communication, September, 2013; Jessica Reeves, Stanford University,

written commun., July 9, 2013; Sneed et al, 2013). These areas are a 1,200 mi2 subsidence bowl

near El Nido (south of Merced, and west of Madera ) and a larger bowl, about 2,700 mi2, west of

Tulare and east of Kettleman City (Figure 7). Currently subsiding areas shown on Figure 7 are

shifted substantially from the locales of major subsidence during 1926-1970. Studies and

planning efforts associated with the San Joaquin River Restoration Program have made much

more information available in the northern subsidence bowl than in the southern bowl to describe

specific instances of infrastructure problems related to current subsidence in the San Joaquin

Valley. These include:

The northern subsidence bowl: El Nido (Figures 5, 7). Subsidence rates in the El Nido area are

currently about 20 times the rate of average historical subsidence in this area. The U. S. Army

Corps of Engineers (USACE) predicts that

17 feet of subsidence will occur in the

northern subsidence bowl during 2000-

2060.

Sack Dam—Design and construction challenges. Surveys by DWR contractors found 0.6

feet of subsidence near the Sack Dam during 2008-2010. InSAR analysis by NASA-JPL

during 2007-2011 determined that more than 1 foot of subsidence had occurred near the

Sack Dam. Surveying by the USBR associated with redesign of the Sack Dam as part of

the San Joaquin River Restoration Program determined that subsidence near the dam

continued at a rate of about 0.5 ft/yr during 2011-2013. These discoveries halted planned

construction and design efforts for the $25 million project, as agencies considered how to

adapt to the lowered land surface and prepare for likely continued subsidence.

San Joaquin River—Reduction in flow capacity. Results of InSAR analysis and

surveying showed at least 1.8 feet of subsidence near the San Joaquin River between

2008 and 2010. Subsidence causes flow channels to sag, erosion at the upstream end of

the sag and sediment deposition in the sagged area. Subsidence likely has reduced the

flow capacity of the San Joaquin River west of El Nido to less than half its design

capacity of 1,500 ft3/s (Reggie Hill, Lower San Joaquin Levee District (LSJLD), oral

commun., December 11, 2013).

Eastside Bypass—Reduction in levee freeboard, reduction in flow capacity, increased

extent of flooding. InSAR analysis and surveying show 1.8 feet of subsidence near the

Eastside Bypass during 2008-2010. In 2008 the flow capacity of one reach of the bypass

was 5,000 ft3/s lower than the designed capacity, 17,500 ft

3/s. Modeling studies by DWR


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predict that subsidence continuing at current rates will reduce levee freeboard by an

additional 1.5 feet between 2011 and 2016 reducing the flow capacity of this reach to

10,000 ft3/s. The USACE predicts that a flood breaching the west levee, which had

subsided more than the east levee, would inundate at least 32 mi2 and possibly as much as

170 mi2 west from the bypass.

Highway 152—Surveying by California Department of Transportation (Caltrans)

indicates that Highway 152 has subsided about 5.3 feet during 1972-2004 (Figure 5B).

The highway likely continues to subside along with all other surface infrastructure in this

subsidence bowl.

California High Speed Rail (CHSR)—Initial alignment of the Merced to San Jose section

of the planned CHSR indicates that the currently planned alternative routes pass through

parts of the northern subsidence bowl and that the southernmost route of the rail line

traverses the northern edge of the area of maximum subsidence and greatest rate of

subsidence south from Highway 152 (Figure 5A, 7).

The southern subsidence bowl: Tulare-Kettleman City (Figure 7). Maximum subsidence during

2007-2011 was 3.9 feet. The rate of subsidence in this area is similar to and in some places

greater than that of the northern subsidence bowl and extends much more broadly throughout the

San Joaquin Valley. The maximum rate of subsidence here is about twice the maximum rate that

occurred historically in the area. Current known effects include:

Highway 198—Caltrans surveying along Highway 198 (Figure 8) shows that the road

subsided 9.37 feet during 1900s-2004. The highway passes through the northern edge of

the subsidence bowl and so the survey data do not fully capture the maximum subsidence

in this region. Subsidence studies at the Lemoore Naval Air Station (Corbett and others,

2011) indicate that total subsidence there between 1925 and 2010 exceeded 10 feet—

considerably more than the Caltrans survey showed during the 1960s-2004 (3.5-4.0 feet).

Canals—flow capacity has been reduced in many canals in the area and canal check

structures in sagging canals have been rendered marginally useful.

California High Speed Rail—the proposed alignment of the main north to south line of

the CHSR runs directly through the subsidence bowl.


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Figure 8. A) Location of Caltrans surveying profile along Highway 198 in the southern San Joaquin

Valley, and Lemoore Naval Air Station. (Courtesy of California Department of Water Resources.)

Figure 8. B) Elevation changes between the 1960s and 2004 computed from repeat geodetic surveys along

Highway 198. (Courtesy of California Department of Water Resources.)

Water districts, ranchers, and others are dealing with subsidence impacts on water delivery

infrastructure in an information vacuum because there has been no coordinated monitoring of

land subsidence. Were it not for fortuitous satellite radar analyses (NASA-JPL, Stanford

University, USGS) and recent attention focused by the San Joaquin River Restoration Program

planning activities, the breadth and magnitude of subsidence in the area would be unknown.

Much infrastructure in both the northern and southern subsidence bowls potentially could be

impacted by subsidence. Fortunately, federal, state and local agencies have been alerted to the

issues of recent subsidence and can begin to implement appropriate strategies to monitor


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subsidence and minimize its impacts. For example, geotechnical and design engineers now can

adapt plans for design of the CHSR to accommodate potential future subsidence.

2.3 Sacramento Valley

The Sacramento Valley forms the northern one third of the agriculturally rich Central Valley of

California. Although it possesses substantial supplies of surface water, land subsidence in the

Sacramento Valley has occurred when groundwater-levels declined in response to pumping for

irrigation and public water supplies during droughts or in areas undersupplied by surface water.

The earliest subsidence investigations in the southwestern Sacramento Valley were done using

leveling data collected by the USGS and the National Geodetic Survey (NGS) between 1935 and

1964. Land-surface profiles based on these data showed apparent land subsidence of more than 2

feet along a level line between Zamora and Knights Landing in northern Yolo County; more than

1.0 foot near Arbuckle in southern Colusa County; and more than 1.5 feet in central Yolo County

between Zamora and Davis (Lofgren and Ireland, 1973). The area of greatest subsidence is south

of the terminus of the Tehama Colusa Canal, where agriculture developed relying solely on

groundwater for irrigation.

The magnitude of permanent land subsidence observed throughout the southwestern Sacramento

Valley indicates that groundwater levels have dropped below the water level at which inelastic

compaction of aquifer sediments is triggered. An early evaluation of video logs from 317 water

wells and water-level data showed that damaged wells had experienced historically low water

levels. Intact wells either were not experiencing historically low water levels, or were

constructed subsequent to the 1976-1977 drought that had stressed the aquifer system (Borchers

et al., 1998). Drilling and well-services companies reported that “well casings were snapping like

match sticks” throughout the southwestern Sacramento Valley during the 1976-1977 drought,

and that they could not keep pace with the demand for replacement wells.

Damaged wells are located in central Colusa County, through Yolo County, to Dixon in Solano

County. However, the Yolo County Global Positioning System (GPS) network was surveyed

later than the period when most wells were damaged (1976-1977) and does not extend into the

adjacent counties, so it cannot identify the extent of subsidence regionally. Subsidence in the

southwestern Sacramento Valley is a regional problem that cannot be adequately monitored by

local agencies acting independently. Monitoring the magnitude and extent of land subsidence

and its cause, and devising workable solutions to limit future occurrences requires interagency

coordination.


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At Edwards Air Force Base, subsidence caused

sink-like depressions and earth fissures on the

surface of Rogers Lake bed, adversely affecting

the runways on the lake bed that are used for

landing aircraft.

2.4 Antelope Valley

Groundwater accounts for as

much as 90 percent of the water

supply for agricultural and

urban uses in the Antelope

Valley in the western Mojave

Desert east of Los Angeles. In

the city of Lancaster where the

population quadrupled between

1977 and 2010, extensive pumping contributed to groundwater level declines of as much as 300

feet since the 1930s. A regional relationship between land subsidence and groundwater-level

declines in the central Antelope Valley was established on the basis of geodetic and hydrologic

monitoring during 1926-1992 (Ikehara and Phillips, 1994). Subsidence of 6.6 feet at Lancaster

and more than 3 feet at the south edge of Rogers Lake resulted from groundwater pumping that

vastly exceeded recharge to the aquifer system (Figure 9). A 1,969 feet long by 7.5 feet deep

fissure located about 6.8 miles east-northeast from Lancaster was attributed to historical water-

level declines of 245 feet that had occurred prior to its appearance in 1978. At Edwards Air

Force Base (EAFB) groundwater levels declined 150 feet between 1915 and 1991.

At EAFB, subsidence caused sink-like depressions, polygonal cracks, and large earth fissures on

the playa surface of Rogers Lake bed, adversely affecting the runways on the lake bed that are

used for landing aircraft. Numerical modeling also indicated that due to the thickness and low

permeability of clayey confining units, only half the ultimate compaction would occur during the

30 years subsequent to the modeling. Residual inelastic compaction measured during winter

periods in the 1990s is partly caused by the ongoing long-term effects of delayed yield from

thick, slowly draining confining units still responding to large water-level declines between 1950

and 1975. Residual compaction and land subsidence from slowly draining confining units and

clayey interbeds is a legacy of groundwater mining and must be carefully considered in long-

term management of land and water resources at EAFB and elsewhere in the Antelope Valley.

In addition to earth fissures, other negative consequences of land subsidence in Antelope Valley

include altered drainage gradients; increased flooding and erosion; failed well casings; and

structural damage to roads, buildings, pipelines, canals, homes, and other structures. Facing

future population growth and limited options for alternative water sources, water managers in

Antelope Valley are seeking ways to make the best use of currently available resources. Injection

of treated State Water Project water into the aquifer system during the winter (when it is most

available) for later use in the summer (the peak demand period) is one potential element of a

groundwater management plan. The USGS, with local agencies, studied the feasibility of direct

well injection through existing production wells and developed a simulation/optimization model


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to help evaluate the effectiveness of an injection program for halting the decline of groundwater

levels and avoiding future land subsidence while meeting increasing groundwater demand.

2.5 Coachella Valley

The Coachella Valley is located in Riverside County and extends 45 miles from the San

Bernardino Mountains to the northern shore of the Salton Sea. Groundwater has been a major

source of agricultural, municipal, and domestic water supply in the Coachella Valley since the

early 1920s. Groundwater levels declined throughout the Coachella Valley from the 1920s until

1949. In 1948, a large earth fissure formed in the La Quinta area. In 1949, imports of surface

water from the Colorado River to the southern Coachella Valley began, resulting in decreased

pumping and a recovery of water levels in some areas. Since the 1970s, demand for water in the

southern Coachella Valley has exceeded the deliveries of the imported surface water, and water

levels have again declined. The declining water levels have renewed land subsidence in the

Coachella Valley (Sneed, USGS, oral communication, May 30, 2013).

Concerns about land subsidence prompted the Coachella Valley Water District (CVWD) to

contact the USGS to cooperatively establish and operate a land subsidence monitoring network.

InSAR measurements made between June 27, 1995 and September 19, 2010 indicate that land

subsidence ranging from 0.72 to 1.97 feet occurred near Palm Desert, Indian Wells, and La

Quinta (Figure 10). Average subsidence rates in Palm Desert were relatively stable, increasing

Figure 9. Land subsidence in

Antelope Valley between 1930

and 1992 (modified by Galloway

et al., 1998 from Ikehara and

Phillips, 1994).


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from 0.13 ft/yr during 1995-2000 to about 0.15 ft/yr during 2003-2010. Recently, earth fissuring

has reoccurred near La Quinta and differential compaction that damaged homes there has

resulted in litigation. Differential compaction that damaged homes in the Indian Wells area also

has been recently reported. A subsidence profile covering about 27 miles of the Coachella

Branch of the All American Canal showed that the canal had subsided as much as 1.35 feet in the

La Quinta area during June 27, 1995 to September 19, 2010.

The areas that have subsided in the Coachella Valley between 1996 and 2010 are coincident with

locations where groundwater levels declined, both during this period and during most of the past

century. In the northern and central parts of the study area, where substantial subsidence was

measured by 2010, water levels exhibited long-term declines during 1995-2010. The subsidence

in these areas is likely to be mostly permanent because water levels have declined to historically

low levels.

The CVWD has had initial success in halting declining water levels and subsidence in one area

of the valley. In the southwestern part of the valley, subsidence rates slowed or land surface

slightly rebounded during mid-2009-2010 as water levels rose in response to deliveries of

Colorado River water to groundwater recharge facilities. The correspondence between the timing

of increased deliveries and significant water-level recoveries suggests that the water applied to

the recharge ponds is effectively recharging the aquifer system, although reduced groundwater

pumping also can cause water-level recovery. The CVWD is encouraging golf courses and other

landscape irrigators to employ reclaimed water for irrigation purposes. An effective land

subsidence monitoring program helps water managers assess the effects of groundwater recharge

and conservation efforts.


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Unplanned and unmonitored development of

groundwater in desert basins areas has

produced land subsidence.

Figure 10. Areas of subsidence between 2003 and 2005 in the western Coachella Valley as shown by

subsidence contours interpreted from InSAR (modified from Sneed and Brandt, 2013, Fig. 8).

2.6 Mojave River Basin and Vicinity

The Mojave River Basin is located in eastern San Bernardino County. California desert basins

are areas of current or expected

high water demand and are

underlain by thick unconsolidated

aquifer systems. Because surface

water is scarce, groundwater has

been the source of water for agricultural, industrial, and municipal uses throughout the Mojave

Desert since the early 1900s (Sneed et al., 2001). Unplanned and unmonitored development of

groundwater has produced unanticipated land subsidence when aquifer systems transitioned from

elastic deformation to inelastic compaction. The results included an increase in the extent of

inland flooding, damaged engineered infrastructure, and the sudden appearance and erosional

enlargement of destructive earth fissures, which have become permanent features of the

landscape.


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The Fremont Valley, a deep, closed alluvial basin at the southern terminus of the Sierra Nevada

and just north from Antelope Valley, contains an aquifer system composed of as much as 900

feet of sedimentary materials (Holzer, 1984). Prior to 1920, wells in the valley center flowed6; by

1977, water levels in the central part of the valley had declined as much as 243 feet, primarily in

response to increased irrigation pumpage (Holzer, 1984). Subsidence caused by groundwater

withdrawal was documented by Pampeyan and others (1988). Subsidence has tilted the Koehn

Lake playa surface so that when surface water ponds on the playa during storms, it also floods

the area southwest of the playa where subsidence is centralized. Large earth fissures (Figure 11)

also formed in the Fremont Valley (Holzer and Galloway, 2005).

The USGS, in cooperation with the Fort Irwin National Training Center (NTC) in the Mojave

Desert, is investigating the mechanisms driving deformation on the surface of Bicycle Lake

Playa. Bicycle Lake Playa contains the runways used to transport troops and supplies to Fort

Irwin; its stability is of great concern to the NTC. An earth fissure and sink-like depressions

appeared on the playa in 2005 (Densmore, et al., 2010). Giant desiccation cracks have also been

observed. Increased groundwater pumping in the 1990s lowered groundwater levels 82 feet by

2009 and contributed to 0.9 feet of land subsidence during 1993-2006.

Concerns related to the potential for new or renewed land subsidence and fissuring prompted the

Mojave Water Agency (MWA) to contact the USGS to assess land subsidence. The USGS

established a geodetic network of monuments to monitor land subsidence in the Lucerne Valley

using GPS and prepared spatially detailed maps using InSAR to determine changes in vertical

land-surface elevation for the parts of the Mojave River and Morongo groundwater basin that are

managed by MWA.

Groundwater levels in the Lucerne Valley, in the Mojave River watershed east of Victorville,

California, have declined as much as 100 feet since the 1950s. A GPS survey in 1998 indicated

that as much as 2 feet of land subsidence may have occurred since topographic maps were made

in 1969 and 1975 (Sneed et al., 2003). InSAR analysis indicated that the land surface southeast

of the Lucerne Lake playa subsided about 0.3 feet between April 24, 1992 and November 8,

1999 near where groundwater levels had declined 100 feet by the early 1990s. Earth fissures

more than 3 feet in width and depth trend northeast-southwest across the southern playa (Figure

12) (Sneed et al., 2003a).

In 2002, an agreement settled the longstanding issues associated with adjudication of water in the

Mojave River Basin area, establishing thresholds for pumping that helped to reduce groundwater

overdraft. To mitigate subsidence and other effects of overdraft in the Mojave River Basin, the

MWA is using imported California State Water Project (SWP) water for artificial recharge by

6 The term ‘flowing well’ indicates that the water levels in the well are above the ground surface.


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surface spreading. Adjudication, court ordered specification of rights of groundwater withdrawal,

is perhaps the last option available to ensure sustainability of water supplies when other options

have not been successful.

Figure 11. Earth fissure associated

with land subsidence caused by

groundwater pumping in Fremont

Valley, California, March 1978 (from

Holzer and Galloway, 2005).

Figure 12. Earth fissure near the

southeast edge of Lucerne Lake

playa in the Mojave Desert,

California. View is to the northeast,

with a five-gallon bucket for scale.

(Sneed et al., 2003a, Fig. 6 B)


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There is no state or federal agency in

California that has the specific

responsibility to monitor land subsidence.

3.0 MEASURING AND MONITORING LAND SUBSIDENCE

Alarming rates of subsidence recently

have been measured in several areas

of California. This information has

been reported only after the impacts

from subsidence have occurred—

emphasizing the need for increased monitoring. There is no state or federal agency in California

that has the responsibility, or a program in place, specifically to monitor land subsidence.

Consequently, there are no statewide monitoring networks for subsidence. Smaller regional,

county-wide, or local monitoring networks are sometimes constructed to address a specific

subsidence issue. These small networks usually are not geared for long-term monitoring, but

rather operate for a project-specific period of time, usually implemented in reaction to a

subsidence crisis that has damaged essential infrastructure.

There are a few exceptions: adjudicated basins sometimes have management objectives that

require detailed subsidence monitoring and reporting, as do some agencies that are the primary

purveyor of water in a region. If land subsidence monitoring is defined as the systematic and

regular acquisition of information to describe the changing extent and magnitude of the problem,

then most of California must be considered unmonitored.

Viable methods for measuring and monitoring subsidence are briefly discussed below; additional

information is included in the full report (Luhdorff and Scalmanini Consulting Engineers, et al.,

2014, Report of Findings: Land Subsidence from Groundwater Use in California).

3.1 Surveying and the Global Positioning System

Historically, spirit-level surveys7 were used to measure changes in land-surface elevation of

bench marks. In 1995, the Navstar GPS, based on 24 earth-orbiting satellites, became fully

operational, providing continuously available access to at least 6 satellites visible to users in

North America. GPS measurements can be made with portable GPS receivers on a campaign

basis, or can incorporate data from more permanent installations at Continuous GPS sites

(CGPS).

There are more than 800 CGPS sites in California. These sites are unmanned and receive data

from GPS and sometimes other navigation satellite systems. They are installed, owned, and

operated by public agencies, consortiums, and private entities. Several of these entities archive

geodetic information from their own sites and from sites operated by other entities, and the data

7 Spirit-level surveys involve measuring the vertical difference between more than two locations, usually compared

to each other and to a known elevation at a benchmark.


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are available via the Internet. CGPS sites are used as components of land deformation

monitoring networks that primarily show the horizontal movement of tectonic plates. Because

very few CGPS were installed with the intent to monitor land subsidence, few are optimally

located for that purpose.

Although they own and operate only one CGPS site in California, the NGS archives and provides

on their website for x, y, and z coordinates as well as time-series data for approximately 284

CGPS sites in California (Figure 13) that were constructed and are operated by other agencies or

consortia. These sites form the Continuously Operating Reference Station (CORS) network of

the NGS. The CORS network data add much-needed insight into the daily, seasonal, and climatic

variations of land surface elevations, which can be related to groundwater levels and extraction.

Figure 13. Continuously Operating Reference Station

(CORS) Network, retrieved from NGS September

16, 2013.


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InSAR provides more detailed subsidence

information over larger areas than can be

measured by any other known technique.

3.2 Satellite Synthetic Aperture Radar Interferometry (InSAR)

InSAR is an invaluable satellite-based

remote-sensing technique that uses

radar signals to measure land-surface

deformation at an unprecedented level

of spatial detail and high degree of

measurement resolution. InSAR can provide more detailed subsidence mapping over larger areas

than can be measured by any other technique. Measurements can be done entirely retroactively,

by acquiring historic (1992 to present) repeat satellite Synthetic Aperture Radar (SAR) data sets

for the area of interest, and then processing the SAR data using interferometric techniques to

determine changes in elevation over large areas with a precision of a few millimeters. Much of

the Earth was repeatedly surveyed by the SAR satellites for establishing digital elevation models

and to detect deformation associated with earthquakes, volcanoes, and glaciers. Those data sets

provide the early basis for InSAR. Unfortunately, analyzing long-term SAR data can be difficult

because of the short life spans of the satellites (i.e., they are generally decommissioned after

about 5 years of service). The United States does not have a civilian SAR satellite, so presently

data must be purchased from international sources (e.g., Canada, Germany, Italy, Japan, and

Europe).

Under ideal conditions InSAR can detect surface deformation of less than half an inch over

hundreds of square miles, at a spatial resolution of 295 feet or better (Sneed et al., 2013). Radar

signals generated from a satellite are bounced off stable radar reflectors on the Earth’s surface,

such as roads, buildings, other engineered structures, mountains, and undisturbed ground and

rocks. The travel time of the radar signal from the satellite to the ground and back to the satellite

is proportional to the distance between the satellite and the ground. Subtracting, or interfering,

the data collected by a satellite passing over the Earth at different times provides the information

needed to prepare interferograms and interpret subsidence magnitude.

The quality of SAR data and the usefulness of interferograms can be affected by atmospheric

conditions (fog and clouds), land-use, satellite orbit geometry, ground cover, and topographic

relief. Methods have been developed to identify and discard, or correct for SAR images with

these issues. InSAR techniques have provided invaluable tools for remotely assessing large areas

with a high degree of measurement resolution, especially in California. InSAR techniques must

be integrated with ground-based geodetic surveying for ground-truthing and to provide

continuity of subsidence monitoring during periods when conditions are unsuitable for InSAR or

when satellites are inoperable.


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3.3 LiDAR

LiDAR is a remote sensing technology that measures distance by illuminating a target with a

laser and analyzing the reflected light. LiDAR has been used extensively both in tripod-mounted

ground scanning and in airborne mapping surveys. LiDAR collects measurements independent of

weather conditions or time of day, but it is limited to line-of-sight measurements unless a target

is scanned from different vantage points. Tripod mounted LiDAR provides distance from the

instrument to millions of points on the land surface with a resolution of at least 0.39 inches.

Airborne LiDAR has been of invaluable assistance in geologic mapping and understanding

geomorphic processes that shape the land surface. There are many potential sources of error in

elevations acquired by airborne LiDAR: LiDAR equipment, interpolation, horizontal

displacement, flight height, terrain slope, and ground cover all influence LiDAR-determined

elevations (Hodgson and Bresnahan, 2004). Airborne LiDAR measurements have a lower

vertical resolution compared to other methods of measuring the elevation of the land surface.

3.4 Borehole Extensometers

Borehole extensometers measure the continuous change in vertical distance between the land

surface and a subsurface reference point, usually the bottom of a well (Riley, 1986). Several

different kinds of borehole extensometers have been used to measure aquifer-system compaction,

including pipe, cable (steel), rod, and magnetic/radioactive marker. Fiber-optic components for

borehole extensometers have been proposed. Pipe and steel-cable extensometers are most

common and have been used extensively in California. Aquifer-system compaction measured

using extensometers can be used to determine whether groundwater extraction from a particular

part of the aquifer system may be contributing to land subsidence. These measurements can be

compared to measurements of total land subsidence at the site (e.g., as determined from

surveying, co-located continuous GPS sites, or InSAR) to determine whether processes other

than aquifer-system compaction, such as hydrocarbon extraction, are also contributing to land

subsidence. Extensometers must be paired with several, short-screened, water-level monitoring

wells, called piezometers, to detect the onset of inelastic compaction for management purposes

and to calculate important mechanical and hydraulic properties of the aquifer system.

4.0 RECOMMENDATIONS

The following summary recommendations are provided to help California address the ongoing

economic and environmental impacts associated with over extraction of groundwater and

resulting land subsidence. A complete set of recommendations is contained in the full report

(Luhdorff and Scalmanini Consulting Engineers, et al., 2014, Report of Findings: Land

Subsidence from Groundwater Use in California). Only by monitoring and evaluation of

monitoring data can California avoid the potential costly impacts of land subsidence that have

plagued the state in the past. This report presents the technically necessary and desirable


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measures. An economic analysis should be done to determine the most cost-effective set of

actions to limit and address future subsidence.

4.1 Monitor Land Surface Elevation Changes and Compaction

Remote Surveillance and Analysis: InSAR and Continuous GPS

InSAR provides the most cost efficient method to generate high-resolution land surface

deformation information over large areas with high spatial detail. InSAR products provide

detailed monitoring data and imagery that facilitates communicating the magnitude and extent of

subsidence to the general public. Although the United States does not have a civilian radar

satellite that can provide data for InSAR analysis, NASA and the Indian Space Agency are

cooperating to construct and launch a SAR satellite this decade.

All available SAR data covering unconsolidated aquifer systems in California should be acquired

and analyzed to identify areas of potential aquifer compaction, especially in areas of critical

infrastructure. Additionally, continuous GPS data should be examined for likely deformation

sources and correlated with InSAR results. New CGPS stations should be installed in areas of

actual or potential subsidence.

Ground Surveillance and Analysis: Surveying and Borehole Extensometry

Ground surveillance techniques are a critical component in identifying areas of subsidence, and

are an important complement to the remote techniques described above. Therefore, geodetic

surveys should be correlated with InSAR and CGPS data and with groundwater-level data.

Geodetic networks should be improved by upgrading and protecting geodetic monuments.

Borehole extensometers provide important aquifer compaction data. The distribution of

extensometers in groundwater basins and subbasins should undergo a comprehensive evaluation

and abandoned extensometers should be refurbished in priority areas. New extensometers should

be designed and installed to monitor likely compacting intervals in areas where InSAR, CGPS,

surveying, or infrastructure effects indicate that subsidence is occurring, or where groundwater

use is increasing. Extensometers should be paired with multi-depth monitoring wells

(piezometers) and a CGPS installation. New and more economical methods of building

extensometers should be tested and assessed.

4.2 Characterize Aquifer System and Monitor Groundwater Levels

Declining groundwater levels can trigger permanent land subsidence; it is therefore important to

monitor, compile, and interpret groundwater levels throughout the state. The collection and

storage of groundwater-level data by all federal, state, and local entities should be coordinated

and made publically available. The distribution of groundwater-level monitoring wells areally


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and vertically within the aquifer system should be assessed to identify locations where additional

monitoring wells are needed to track changes in hydraulic head. In order to make groundwater

level monitoring measurements meaningful, and to use these measurements to understand the

response of the aquifer system to natural stresses (e.g., precipitation and droughts), imposed

stresses (e.g., pumping and artificial recharge) and the potential for land subsidence, requires that

the construction of monitored wells and the distribution of fine-grained sediments be understood

in the context of the aquifer system.

4.3 Collect, Store and Disseminate Data

Data collection related to subsidence, and the interpretation of such information, is fragmented. It

is critical to develop a state repository for subsidence-related information. Currently, collection,

storage, dissemination, and reporting of the data required to monitor and evaluate land

subsidence is dispersed among many federal, state, and local agencies. Coordinated data

maintenance should be achieved to assure consistent procedures for the collection, storage, and

availability of pertinent water-resources data. The Arizona Department of Water Resources

(ADWR) has developed a land subsidence monitoring program (Conway, 2013) that could

provide a model for implementing a statewide subsidence-monitoring program in California.

Alternatively, regional coordination of these responsibilities and an ongoing repository for the

storage and disbursement of these data would facilitate their efficient use by government

agencies, water purveyors and their consultants, and the public.

4.4 Evaluate and Prioritize Subsiding Groundwater Basins

If the above data were in available databases and archives, groundwater basins statewide could

be more easily and consistently prioritized for subsidence-relevant planning. In priority basins,

where subsidence has occurred or is likely to occur, a step-wise planning assessment and

management program could proceed as follows:

Evaluate historical groundwater-level monitoring information and establish augmented

groundwater-level monitoring networks to fully characterize the aquifer system.

Characterize land surface deformation in priority basins with InSAR techniques, follow-

up with geodetic surveys in subsiding areas, and establish a network of CGPS stations to

provide time-series data at critical points.

Establish borehole extensometers and associated multi-level monitoring well arrays to

measure compaction and hydraulic head in various depth intervals of the aquifer system

and CGPS installations to measure total change in land surface elevation at each

extensometer.


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Establish measurable basin management objectives (BMOs) that identify goals for

groundwater levels, land-surface elevations, and rates of change of each to avoid amounts

or rates of inelastic compaction judged to be inappropriate for efficient operation of local

infrastructure. These BMOs could be implemented through pumping strategies, artificial

recharge, conservation strategies, and other sustainable groundwater management

alternatives.

Documents

Summary Report / April 2014 Land Subsidence from ... · Summary Report / April 2014 Land Subsidence from Groundwater Use in California Acknowledgement The California Water Foundation